 Welcome back MechanicalEI! Did you know that many elements like factor of safety, the actual power to be transmitted and transmission distance help decide the classification of police? This makes us wonder, how are police classified? Before we jump in, check out the previous part of this series to learn about what pedestal and footstep bearings are. Now, there are three main types of police based on the type of belts that run through them. V-belt pulleys are designed for light-duty power transmission and high performance conveying. They are best suited for applications with smaller pulleys and large central distances. These pulleys have a high power transmission efficiency, are cost-effective and are easy to use and install. A V-belt pulleys is a unique mechanical linkage with a cross-section that resembles an isosceles trapezoid. The V-belt and its complementing pulleys create the most efficient belt drive known. However, V-belt pulleys are solely used for transmitting power between two parallel axes, as misalignment between the axes considerably decreases the efficiency due to friction losses. Round belts are pulleys with a 60-degree V-groove designed to run a circular cross-section belt. Round pulleys are only suitable for idler pulleys that guide the belt or when o-ring type belts are used. The V-groove transmits torque through a wedging action, thus increasing friction, enabling round belt pulleys to be used in low torque situations only. A fast and loose pulleys arrangement is used on shafts to enable a machine to be started or stopped at will. A fast pulleys is key to the machine shaft while the loose pulleys run freely. To transmit power, the belt runs over the fast pulleys and when the power is not needed, the belt is simply pushed over or bypassed to the loose pulleys, which then rotates freely. This arrangement of pulleys is very important in paper mill industries, where stopping of one machine should not interfere with the other machines, which are run by the same line shaft. Shown here is one such pulleys system with loose pulleys on the extreme left. Hence, we first saw how pulleys are classified based on the type of belts that run on them, and then went on to see what fast and loose pulleys are. Also, thanks a lot for those constructive comments. You helped the channel grow. So, here are the top mechanical e-eyes of our last videos. In the next episode of Mechanical E-Yang, find out what pipe joints are.